Improved measurement of absolute branching fraction of the inclusive decay ${\mathrm{\Lambda }}_c^{+}\to K_S^{0}X$

By analyzing $4.5$ fb${}^{-1}$ of $e^{+}{e}^{-}$ collision data accumulated with the BESIII detector at center-of-mass energies ranging from $4599.53$ MeV to $4698.82$ MeV, we report the measurement of the absolute branching fraction (BF) of the inclusive decay ${\mathrm{\Lambda }}_c^{+}\to K_S^{0}X$ using the double-tag technique. The result is $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to K_S^{0}X)=(10.9\pm 0.2\pm 0.1)\mathrm{\%}$, where the first uncertainty is statistical and the second is systematic. This result indicates that there are still undiscovered decay channels containing $K_S^0$ in the final state with a combined BF of $(3.1\pm 0.4)\mathrm{\%}$. The BF of the inclusive decay ${\mathrm{\Lambda }}_c^{+}\to {\bar{K}}^0\mathrm{/}{K}^{0}X$ is calculated to be $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to {\bar{K}}^0\mathrm{/}{K}^{0}X)=(21.8\pm 0.4\pm 0.2\pm 1.1)\mathrm{\%}$, where the third uncertainty accounts for a possible difference between $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to K_S^{0}X)$ and $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to K_L^{0}X)$. The result is in agreement with the prediction of the statistical isospin model.